We report deposition parameters for improved electrochromic behavior of reactively sputtered iridium oxide films (SIROF's). When operated in electrolyte, SIROF's deposited under these conditions may be bleached to a state exhibiting, to within experimental error (<0.4%), zero transmission loss in the visible. SIROF's which can be fully colored to an optical density (OD) of 0.45 (single pass), show a response time for coloring or bleaching (through a ΔOD of 0.3) of 40 msec under constant voltage address. This may be reduced to 20 msec in each direction if IR compensation is employed. Preliminary data show no difference in color/bleach cycle lifetime from that of SIROF's deposited under slightly different conditions. No change in contrast is perceivable after cycles at room temperature.